I think it would still be sai, or even ei. This chart helped a lot during this section... https://www.duolingo.com/skill/ro/Possessives/tips-and-notes
In order for you to use the word 'sale' (which can be used for both 'his' and 'her' - confusing right!? hah) the sentence would have to be about something feminine, such as 'tomatoes'... "Rosiile sale nu sunt bune." That translates to "His/her tomatoes are not good."
There seems to be a lot of overlap according to that chart which makes it very confusing for me. You can say His carrot, or His carrots and it seems like you'd be able to use 'lui' for both and that would make sense.
I hope I didn't confuse you more! And I hope what I said was correct!
I like how the speaker said "sînt buni" rather than "sunt buni" and it turns out you may catch older Romanian speakers using the former -- my dad, for instance.
Fun fact: the official decision to replace "sînt" in the verb conjugation for "a fi" with "sunt" was made in the '90s or '00s... I'm not sure which decade.